Hybrid powertrain systems generate propulsion torque from two or more energy sources, e.g., hydrocarbon-based fuels through an internal combustion engine, and electric power through one or more electric machines, with the propulsion torque transferred through a geartrain to an output member that is coupled to a driveline.
Control systems for operating hybrid powertrain systems control torque outputs of the engine and electric machine(s) and apply torque transfer elements in the transmission to transfer torque in response to operator-commanded output torque requests, taking into account fuel economy, emissions, drivability, and other factors. A control system monitors various inputs from the vehicle and the operator and provides operational control of the hybrid powertrain, including controlling transmission operating mode and gear shifting, controlling torque outputs from the engine and electric machine(s), and regulating the electrical power interchange among the electrical energy storage device and the electric machines to manage outputs of the transmission, including torque and rotational speed.
Hybrid powertrain systems may operate in an electric vehicle (EV) mode, wherein all propulsion torque is generated by the electric machine(s) with the internal combustion engine in an OFF state, and electrically-variable modes (EVT), wherein the internal combustion engine is in an ON state and may generate some or all of the propulsion torque, or may be transferred to an electric machine to generate electric power that is transferable to the electric machine(s) to generate propulsion torque.
Operating a hybrid powertrain system in the EV mode may enhance customer satisfaction. However, operating in the EV mode at or near system limits for such operation may reduce customer satisfaction related to engine startability and tip-in response.